1. Field of the Invention
The present invention relates to a method for covering a substrate with an essentially biodegradable protein foam barrier. More particularly, the present invention relates to a method for providing protein containing foam coverings to substrates such as landfills, sewage holding tanks, contaminated soil sites, sludge deposits, compost piles and the like, to effectively form a semi-permanent foam layer between the exposed surfaces of such substrates and the environment surrounding them.
In an alternative embodiment the present invention also relates to a method for providing a foam covering to substrates such as buildings and other natural and artificial structures to protect such substrates from adverse environmental conditions such as polluted air or water, insects, extreme hot and cold temperatures, toxic vapors and the like. For example, it is often desirable to provide a protective foam barrier layer on the exposed surfaces of buildings or houses thought to be in the path of forest or brush fires.
In another alternative embodiment the present invention can be used to enhance the action of "oil-eating" bacteria used in the clean-up of petroleum spills by acting as a medium to hold the bacteria in contact with the spilled oil.
Although the method and apparatus described herein may be readily applied to all of the substrates recited above, for simplicity and convenience, this invention will be described in connection with its application as a covering for a landfill waste site. In this application the protein containing foam is used as a substitute for the dirt cover customarily applied to such landfills. It is to be understood, however that the description of this invention as applied to a landfill is merely intended in an illustrative sense and is not to be limited to a single application.
2. Background of the Invention
In the United States, the dumping of waste as in commercial and municipal landfills is regulated by state, local and federal regulations which generally require that the surface of the landfill, containing the day's deposit of waste, must be covered on a daily basis. Typically, such regulations require that the waste on the exposed surface of the landfill (the working face) must be covered by a six inch layer of earth. These regulations are designed to reduce the spread of disease and trash by insects, vermin, birds, etc. by limiting their access to the garbage. Covering the day's refuse also serves to reduce odor and polluting vapors and fumes.
This requirement for covering the day's refuse places a heavy burden on the landfill operators by requiring a substantial amount of labor and equipment to accomplish the daily covering operation. The requirement is also costly to the environment as the available landfill space is rapidly depleted. The addition of six inches of earth daily effectively uses up a great deal of available space within the landfill which could otherwise be used to contain more waste. With available space being rapidly depleted and land prices increasing, this will certainly become an even greater burden in the future.
This problem has been previously addressed in U.S. Pat. Nos. 4,421,788 to Kramer and 4,519,338 to Kramer et al. which disclose use of a hardenable plastic foam in place of the soil. The processes described in these patents claim it is possible to reduce the thickness of the cover to approximately one to two inches or perhaps slightly less while still achieving an adequate cover to provide the protection required. While a reduction in the amount of wasted landfill area and the labor required for application of the covering is reportedly achieved, these patents make no mention of the environmental effects of the hardenable foam itself. For example, these disclosures are silent as to how long it takes for the foam itself to break down, or as to how much valuable landfill space remains occupied by the hardened foam, or the effect the hardened foam has on drainage parameters within the landfill. Although a great improvement in the amount of waste landfill volume has been achieved, further reduction is desirable as well as improvement in the biodegradability of the foam.
Protein based foam has been used for fire fighting and treatment of hazardous material spills in the past. It is known to use xanthan gums as an additive to such foams as for example described in U.S. Pat. No. 4,424,133 to Mulligan. However, the foam described in this patent is not suitable for use as a temporary cover for the substrates described herein because it lacks the long term stability and is less resistant to rain and wind.
The present invention addresses these needs by providing an improved method and apparatus for covering substrates such as landfills using a protein foam. In addition to the foam composition being readily biodegradable, this composition may actually add to the nutrient value of the soil and help promote biodegradation of the landfill waste as well as adding substantial moisture and some aeration. In essence, due to the unique characteristics of the composition described herein, a foam is produced which is capable of working in harmony with nature.